U.S. Pat. No. 6,079,821 issued to Chwalek et al. discloses a continuous inkjet printhead in which deflection of selected droplets is accomplished by asymmetric heating of the jet exiting the orifice.
U.S. Pat. No. 6,554,410 by Jeanmaire et al. teaches an improved method of deflecting the selected droplets. This method involves breaking up each jet into small and large drops and creating an air or gas crossflow relative to the direction of the flight of the drops that causes the small drops to deflect into a gutter or ink catcher while the large ones bypass it and land on the medium to write the desired image or the reverse, that is, the large drops are caught by the gutter and the small ones reach the medium.
U.S. Pat. No. 6,450,619 to Anagnostopoulos et al. discloses a method of fabricating nozzle plates, using CMOS and MEMS technologies which can be used in the above printhead. Further, in U.S. Pat. No. 6,663,221, issued to Anagnostopoulos et al., methods are disclosed of fabricating page wide nozzle plates, whereby page wide means nozzle plates that are about 4 inches long and longer. A nozzle plate, as defined here, consists of an array of nozzles and each nozzle has an exit orifice around which, and in close proximity, is a heater. Logic circuits addressing each heater and drivers to provide current to the heater may be located on the same substrate as the heater or may be external to it.
For a complete continuous inkjet printhead, besides the nozzle plate and its associated electronics, a means to deflect the selected droplets is required, an ink gutter or catcher to collect the unselected droplets, an ink recirculation or disposal system, various air and ink filters, ink and air supply means and other mounting and aligning hardware are needed.
In these continuous inkjet printheads the nozzles in the nozzle plates are arranged in a straight line, their pitch is between about 150 and 2400 per inch and, depending on the exit orifice diameter, they can produce droplets as large as about 100 pico liters and as small as 0.1 pico liter.
As already mentioned, in all continuous inkjet printheads, including those that depend on electrostatic deflection of the selected droplets (see for example U.S. Pat. No. 5,475,409 issued to Simon et al.), an ink gutter or catcher is needed to collect the unselected droplets. Such a gutter has to be carefully aligned relative to the nozzle array since the angular separation between the selected and unselected droplets is, typically, only a few degrees. The alignment process is typically very laborious if done manually and requires precision-machined components for an automatic kinematic alignment, which results in a substantial increase in the cost of print production labor and cost of the print head. Also, the overall print engine cost is increased because each gutter must be aligned to its corresponding nozzle plate individually with separate kinematic alignment components.
The gutter or catcher may contain a knife-edge or some other type of edge or surface to collect the unselected droplets and that edge or surface has to be straight to within a few tens of microns from one end to the other. Gutters are typically made of materials that are different from the nozzle plate and as such they have different thermal coefficients of expansion. Therefore, changes in ambient temperature can produce sufficient misalignment of gutter and nozzle array to cause the printhead to fail. Since the gutter is typically attached to some frame using alignment screws, the alignment can be lost if the printhead assembly is subjected to shocks and vibration as can happen during shipment or operation.
The U.S. publication 2006/0197810 A1-Anagnostopoulos et al. discloses an integral printhead member containing a row of inkjet orifices.
Earlier coassigned filed application Ser. No. 11/748,663, filed May 15, 2007 titled “An Integral Micromachined Gutter for Inkjet Printhead” and application Ser. No. 11/748,620 filed May 15, 2007 titled “Monolithic Printhead with Multiple Row of Inkjet Orifices” are related to this application and disclose formation of silicon printheads with integral gutters and air channels.
The inkjet printhead is an example of a microfluidic device. Microfluidic devices are devices having a network of channels or conduits or flow paths, or otherwise defined regions of fluid flow, wherein at least one dimension is of order 1 mm or less, and in which fluid must travel for intended operation of the devices. The present invention is also relevant to any microfluidic device in which controlled flow of gases or liquids is required and the flow regimes are such that turbulence causes adverse effects on flow uniformity or control. There is a need to decrease fluid turbulence in microfluidic devices.